In order to reduce the levels of noise and particulate emissions produced by an engine it is desirable to provide an arrangement whereby the rate at which fuel is delivered to the engine can be controlled. It is also desirable to be able to adjust other injection characteristics, for example the spray pattern formed by the delivery of fuel by an injector. It is an object of the invention to provide a fuel injector which permits these requirements to be met.
According to the present invention there is provided a fuel injector comprising a nozzle body defining a bore, an outwardly opening valve member slidable within the bore, the valve member defining a blind bore within which an inwardly opening valve needle is slidable, the valve needle being engageable with a seating to control fuel flow towards a first outlet opening provided in the valve member, and a second outlet opening provided in the valve member, the second outlet opening being in constant communication with a part of the blind bore upstream of the seating and being located such that, in a closed position of the valve member, the second outlet opening is closed by the nozzle body, outward movement of the valve member to an open position permitting fuel delivery through the second outlet opening.
In such an arrangement, with the valve member in its closed position, movement of the needle away from the seating permits fuel delivery through the first outlet opening, thus the injection characteristics, for example the delivery rate and spray formation, are governed by the shape, size and positioning of the first opening. With the valve needle in engagement with its seating, movement of the valve member from its closed position to its open position permits fuel delivery through the second opening thus the injection characteristics are governed by the shape, size and positioning of the second outlet opening.
If desired, the valve member may be provided with a plurality of appropriately positioned said first outlet openings and a plurality of appropriately positioned said second outlet openings.
Conveniently, movement of the valve member is transmitted through the valve needle. In such an arrangement, a bidirectional actuator is preferably associated with the valve needle, the actuator permitting movement of the needle in one direction to permit fuel delivery through the first outlet opening and in an opposite direction to move the valve needle and the valve member to permit fuel delivery through the second outlet opening.